BAGHDAD, (Reuters) – U.S. Vice President Dick Cheney met Iraqi leaders on Wednesday during an unannounced visit to Baghdad, and was expected to press for more progress in meeting political benchmarks aimed at ending sectarian violence.

In Iraq’s relatively peaceful Kurdistan, a truck bomb killed 12 people and wounded 53 in the northern city of Arbil, police said. It was one of the few bombings to hit a region that has been spared the bloodshed engulfing the rest of Iraq since the U.S.-led invasion in 2003.

Cheney’s visit, part of a Middle East tour, could signal growing U.S. impatience at Shi’ite Prime Minister Nuri al-Maliki’s failure to push power-sharing agreements as American military commanders build up troops to secure Baghdad.

John Roberts, the U.S. embassy information officer in Baghdad, said Cheney would also hold talks with General David Petraeus, commander of the 150,000 American troops in Iraq. Roberts gave no further details.

U.S. President George W. Bush, who is sending 30,000 extra troops to Iraq for a security crackdown seen as a last ditch effort to stave off civil war between majority Shi’ites and once-dominant Sunni Arabs, is under mounting pressure from Democrats to show concrete progress in the four-year-old war.

With U.S. troops dying daily in Iraq, American officials have urged the Iraqi parliament to scrap a planned two-month summer recess.

During a visit to Baghdad last month, U.S. Defense Secretary Robert Gates said progress on a package of laws that include a bill dividing up Iraq’s oil wealth would be an important factor in Washington’s decision to maintain higher troop levels.

Petraeus, who last month said Maliki’s cabinet was comprised of leaders with “narrow agendas”, is expected to deliver an assessment of the “troop surge” in September.

Cheney, one of the main architects of a war in which more than 3,300 U.S. troops and tens of thousands of Iraqis have died, arrives in Baghdad at a sensitive time.

Leaders from the Sunni Arab minority have threatened to quit Maliki’s government because they say Sunni interests are being ignored. Washington says a Sunni role in government is needed to bring Sunnis firmly into the political process and tame the Sunni Arab insurgency.

Ethnic Kurds, staunch U.S. allies, have also threatened to block the oil bill in parliament.

The law is another U.S. benchmark, along with legislation to roll back a ban on former members of Saddam Hussein’s party from public office, a plan that has met deep Shi’ite opposition.

Despite the security crackdown, Sunni Islamist al Qaeda has stepped p a campaign of car bombs against Shi’ite targets that officials say are part of a campaign to ignite reprisal killings.

Bomb attacks are extremely rare in Iraq’s autonomous oil-rich Kurdish region, unlike the rest of the country.

Abdul Khaleq Talat, chief of Arbil police, said the blast in the centre of the city was caused by a truck packed with 800 kg (1,764 lb) of explosives covered with kitchen cleaning products.

Talat put the death toll at 12, with 53 wounded.

Arbil is the capital of Kurdistan. The bomb went off near the Kurdish government’s Interior Ministry.

Television images showed Kurdish soldiers and police pulling wounded people from the rubble of a collapsed building. The explosion left a massive crater in the road, damaged vehicles and caused partial damage to buildings. “I was near the site of the explosion. I saw fire coming out from the blast area. A man was burned to death,” a witness said.

A suicide bomber killed more than 60 people at the Kurdistan Democratic Party office in Arbil in May 2005 in an attack that was claimed by a militant Sunni Arab group. That was the last bomb attack in the Kurdish region that residents can recall.